Re: [Qemu-arm] [Qemu-devel] [PATCH] hw/arm/bcm283x: Fix crash with device_add bcm2837 on unsupported machines

[Markus Armbruster]

Peter Maydell <address@hidden> writes:

> On 11 July 2018 at 17:12, Eduardo Habkost <address@hidden> wrote:
>> On Wed, Jul 11, 2018 at 09:21:48AM +0200, Thomas Huth wrote:
>>> Hm, ok, so how to continue here now? Shall we at least mark the
>>> bcm2836/7 devices with user_creatable=false, so that users can not crash
>>> their QEMU so easily with device_add? The problem with introspection via
>>> device-list-properties would still continue to exist, but I think that's
>>> less likely used in practice... otherwise we could still move the
>>> qdev_set_parent_bus() calls to the realize() function instead, and just
>>> add a big fat FIXME comment in front of the code block, so that we
>>> remember to clean that up one day...
>>
>> Crashing device-list-properties should be a blocker bug, IMO.

Seconded.

>> Moving to realize is not the best solution, but I would prefer to
>> do that in 3.0 instead of leaving the device-list-properties
>> crash unfixed.
>
> I would like to see the crash fixed too. But I'd like to
> see it fixed:
>  (a) by having clear documentation about how the QOM
> system works, what you should do in init and what you
> should do in realize, when and why you need to manually
> parent objects, etc
>  (b) as far as possible making our APIs for doing this
> easy to use correctly and difficult to use wrongly. At
> the moment we have APIs that are far too easy to misuse,
> which means we will continue to get bugs like this and spend
> a lot of time on one-off fixes for them.
>
> In particular I don't understand why we need to manually
> parent these objects at all.

I want both (a) and (b) as badly as anyone, but we should not hold any
particular crash bug hostage to get them.